1. Field of the Invention
The present invention relates to a tracking error signal detecting apparatus using an electron beam which can be utilized in an information recording-reproducing apparatus, or the like.
The present invention also relates to an apparatus for effecting recording/reproduction of information by the utilization of a plurality of electron beams in which electron beams are applied to a recording medium to record information on the recording medium or electron beams are applied to a recording medium having information recorded thereon to reproduce information from the recording medium.
2. Related Background Art
Optical disk devices represented by video disks and optical card devices may be mentioned as typical information recording-reproducing apparatuses. A basic tracking error detecting system used in an optical disk device will hereinafter be described with respect to an example of the prior art shown in FIG. 1 of the accompanying drawings.
In FIG. 1, DSK designates an optical disk on which pits are recorded. Along the optical path of a laser beam emitted from a semiconductor laser LDI, there are disposed a beam slitter BS for directing the reflected light from the optical disk, DSK to a two-division photodetector TDPD, a collimator lens CL, and an objective lens SL for condensing the laser beam into a spot of about 1 .mu.m.phi. on the optical disk DSK. The two-division photodetector TDPD is provided in the direction of the reflected light by the beam splitter BS, and the output signal thereof may be input to a differential amplifier DA.
In such an arrangement, if a pit PIT on the optical disk DSK is toward the right, with respect to the laser beam spot LBS, as shown in FIG. 2A of the accompanying drawings, the quantity of light received by the left half photodetector TDPDL of the two-division photodetector TDPD will increase, and conversely, if the pit PIT on the optical disk DSK is toward the left, with respect to the laser beam spot LBS as shown in FIG. 2B of the accompanying drawings, the quantity of light received by the right half photodetector TDPDR of the two-division photodetector TDPD will increase. When the pit PIT on the optical disk DSK is properly at the center with respect to the spot LBS as shown in FIG. 2C of the accompanying drawings, the quantities of light received by the left and right photodetectors TDPDL and TDPDR become equal to each other. So, by comparing the two left and right outputs of the two-division photodetector TDPD, the amount of relative positional deviation between the pit PIT and the spot LBS and the direction of the deviation can be detected, and a signal differentially amplified by a differential amplifier DA is used as a tracking error signal TES.
However, in the method of obtaining a tracking error signal by the use of the laser beam represented by this example of the prior art, it is difficult to step down the diameter of the spot LBS to 1 .mu.m.phi. or less and therefore, it cannot be expected in the future to obtain a tracking error signal TES of higher accuracy. Thus, it is difficult to accomplish highly dense recording in which the track pitch of the optical disk DSK is further reduced from the present order of 2 .mu.m.
Also, in the method using such a laser beam, use is made of numerous optical parts of high accuracy, including a beam splitter and lenses and therefore, such a method requires a high cost and great volume. Furthermore, generally, the S/N ratio of the tracking error signal TES obtained by such a method is low. Therefore, a relatively high-degree technique is required for signal processing and also, highly accurate positioning of the individual optical parts is necessary. Also, when the laser beam is finally to be minutely moved on the pit PIT, such movement is effected by mechanically moving the optical parts by means of an actuator, and this limits the response frequency, which also forms a great impediment for accomplishing highly accurate tracking.
On the other hand, besides the apparatuses for effecting the recording/reproduction of information by the use of a laser beam, such as optical disk devices, an example of the apparatus for effecting the recording, reproduction and erasing of information by the use of an electron beam is described in a journal Shinku (Vacuum), Vol. 26, No. 4, 1983. The apparatus described in this journal is such that relative to a memory layer comprising an MOS structure, an electron beam is deflected by deflecting means, whereby the electron beam is applied to any pit on the memory layer to thereby accomplish the recording, reproduction and erasing of information. However, this apparatus is not provided with means for determining whether the electron beam is accurately irradiating the designated pit and therefore, cannot accomplish accurate recording, reproduction and erasing.
In addition to the reason set forth above, the use of a single electron beam has made the conventional electron beam memory device unsuitable particularly for providing a great capacity.